Add correct stub for _GzipReader

Author: rhpvorderman

src/isal/isal_zlib.pyi

@@ -5,7 +5,6 @@
 # This file is part of python-isal which is distributed under the
 # PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2.
 
-import io
 import typing
 
 ISAL_BEST_SPEED: int
@@ -65,5 +64,14 @@ def compressobj(level: int = ISAL_DEFAULT_COMPRESSION,
                 zdict = None) -> Compress: ...
 def decompressobj(wbits: int = MAX_WBITS, zdict = None) -> Decompress: ...
 
-class _GzipReader(io.RawIOBase):
-    def __init__(self, fp: typing.BinaryIO, buffersize: int = 32 * 1024): ...
+class _GzipReader():
+    def __init__(self, fp: typing.BinaryIO, buffersize: int = 32 * 1024): ...
+    def readinto(self, obj) -> int: ...
+    def readable(self) -> bool: ...
+    def seekable(self) -> bool: ...
+    def tell(self) -> int: ...
+    def seek(self, offset: int, whence: int): ...
+    def close(self): ...
+    def readall(self) -> bytes: ...
+    def read(self, __size: int): ...
+    def flush(self): ...